Breaching Security

Background
"I must kill Gaius Maro, an agent of the Emperor's security force. Once he's dead, I must plant a letter on his body that will incriminate him in a plot to kill the Emperor. If I wish to earn a bonus, I must not kill him in Dragon Bridge, or on the road, but in one of the cities he visits."

Walkthrough
To receive the bonus item, Olava's Token, Gaius Maro must be killed in a major city. Travel to Dragon Bridge and steal his schedule. Try to meet up with him in Riften. Enter the alleyway to your left after fast traveling to Riften (you may need to pick the lock on the gate). Shoot an arrow from the alley at Maro as he leaves (around 11PM) in order to avoid detection and any bounty. If you are a low level, he may not die with one sneak attack, so be prepared for a fight. Another option is to wait in the corner of Riften castle's courtyard, behind the small grouping of trees, and wait for him to exit (he exits that side every time at around 1:30 A.M. Actual times may vary). He will be alone and far enough away from any guards to allow you to kill him without any worry about bounty.

Palace of the Kings (or other Barracks)
Gaius Maro will sleep in the barracks with the guards in Windhelm. This can be one of the hardest places to get him without being detected. Wait until ten PM in the corner by the sleeping guard and equip a bow, and, if possible, coat the arrows with poison. Fire an arrow at Maro. Each time he will get up and look around the room, and can be continually shot without being discovered. Warning: The guards in the beds will get up and look too sometimes, but will not see you in the shadows. After Maro is dead, wait till the guards settle down and then creep over to his body and plant the note. Sneak back to the corner. Jump over the beds with the guards in them until you reach the doorway, then sneak out to freedom.

The Bannered Mare
In Whiterun, it is extremely easy to sneak into his bedroom in The Bannered Mare, as it seems to be the only time he isn't bunking in a castle or in barracks, and kill him in his sleep with the door shut. Then you may plant the letter. This does not result in a bounty at Whiterun, and you will receive the bonus token from Gabriella.

Approaching him directly
Another alternative method is to approach Gaius Maro and use the option of telling him how you'll kill him, and then the Emperor. After this, he will begin to attack you. You can then fight back without obtaining a bounty. This method can be used in any major city in order to receive the bonus. If using this method, it's best to confront him in view of a guard - so that it is seen that Gaius attacks you first. If a guard wanders into view of the fight as it's proceeding and the first blow he sees is struck by you, you will earn a bounty. (Occurred on PC version, while using a paralysis weapon - guard wandered into view and saw me attack Gaius while he was paralyzed, and a bounty was earned.)

Bonus
The bonus can also be received just outside a city. If you are lucky enough to be attacked by a dragon just outside a city, you can kill him while the guards are fighting the dragon and no bounty will be placed on you. The bonus will still be counted.

Dragon Excuse

An easy way to kill Gaius is to go to Dragon Bridge until a dragon appears. Do not slay the dragon until Gaius is dead. this way, the soldiers won't fight you and you get a dragon soul.

Pickpocket

For all those with light fingers, it should be noted that it is possible to plant the incriminating letter on Gaius before killing him and have the quest complete as normal. This allows him to be killed at range and in the open, with the player slipping away without approaching his body.

Conclusion
Upon returning to the Dark Brotherhood Sanctuary, you are approached by Gabriella who initiates dialog, congratulates you on completing the mission, and gives you whatever reward you are due. This completes Breaching Security and automatically starts The Cure for Madness, in which you find something has gone wrong in the Sanctuary......

Gauis Maro's Schedule

 * Morndas - Solitude, the Emperor's Tower
 * Morndas Evening - Solitude, Castle Dour (food and sleep)


 * Tirdas - Windhelm, the Palace of the Kings
 * Tirdas Evening - Windhelm Barracks (food and sleep)


 * Middas - Riften, Mistveil Keep


 * Turdas - Whiterun, Dragonsreach
 * Turdas Evening - Whiterun, the Bannered Mare (food and sleep)


 * Fredas - Markarth, Understone Keep
 * Fredas Evening - Markarth, guard tower (food and sleep)


 * Loredas & Sundas - To be spent at your discretion
 * Repeat (until I have recalled you personally)

The guards and Jarls of the cities have been informed of your arrival, and will leave you to your work. Study the guard patterns, examine any entrances and exits, and make note of any irregularities.

Talk to no one - the fewer people who know about your mission, the safer the Emperor will ultimately be.


 * Oddly enough, his father Maro informed Windhelm (the Stormcloak Headquarters) of his son's arrival.
 * Detection of the player can cause Gauis Maro to deviate his schedule, even if the player doesn't talk to him. Plan accordingly, simply waiting for him in one city where he's supposed to visit may be the way to go.

Bugs

 * Gaius Maro and his companion might attack instantly when the player enters Dragon Bridge, meaning that you can't follow him to a city and you immediately lose the bonus. Currently there is no patch. Reloading an earlier save prior to starting the quest has been known to work.
 * You might not receive the Incriminating Letter at all. No known fix so far. Sometimes doing another quests helps, the Incriminating Letter appears in your inventory (worked on pc for me).
 * The dialogue option to turn in this quest occasionally doesn't show up. Instead, she'll say "Gaius Maro still lives. I assumed you were more competent." This can be Quite annoying. So far, there isn't a known patch.
 * If you attempt to kill Gaius Maro using the console, he will act as if immortal and simply fall to the floor, only to rise on full health. If you must kill him with the console use "tgm" to toggle god mode, and then kill him as you would.
 * Solution: Get caught by a guard, pay the fine, travel back and they wont attack. Cost: 1030 . This is from killing the woman in the previous quest)[Confirmed for the 360 as well, make sure you're not wearing the Ebony Mail, and as soon as you appear in Dragon's Bridge from fast travel, run to your left behind the building. Find a guard away from Gaius, pay your fine, and fast travel back.
 * Possible Bug: It has been reported that if you complete the Stormcloak questline before performing this quest, Stormcloak guards in Dragon Bridge will attack the Maro's and stay hostile after killing them, thus leaving you unable to continue the quest. However on my playthru, (02/20/12) on version 1.3.10 I have found this to not be the case. I completed the full Stormcloak questline with the finish in Solitude and the Stormcloak guards in Dragon Bridge took no special notice of the Maro's and the quest continued normaly.
 * Gaius Maro will not leave Dragon Bridge until after you listen to him talk to his father and the woman. Make sure to stay there until he begins walking, and steal the schedule, before attempting to wait for him in another town.
 * In Winterhold's palace barracks, Gaius Maro can be killed without the need to engage in combat. To do this, shoot him while hidden in a corner of the barracks then let him hit you once. The guards will attack Maro but will not kill him, you can kill him by shooting him again while hidden and you will still get the bonus for killing him in a major hold. Note that none of the guards will attack you, but after you finish him off one guard may fight you, simply run out of the city and no bounty will be placed on your head.
 * Whenever Gaius Maro sees you he begins taking an alternate route. This can make the quest quite hard as he will turn away from a city if he sees you anywhere near it. I suggest just waiting in a tavern in Whiterun as he will follow his normal journey until you appear out of it. Then, kill him anywhere in Whiterun and use your position as Thane to remove the bounty placed on you.
 * upon arriving at Dragon's Bridge, you may encounter a dragon. Maro will not be killed by the dragon, but soon after his conversation, he will begin to walk down the road. You can follow him to level up your sneak skill, but you'll find yourself in some pretty weird places. He often walks away from the road and then wanders back to it, and at some points even goes for a swim in deep water, where he may be bitten by Slaughterfish.

Breaching Security