LONDON -- A man convicted of murder for beating a homeless man to death climbed over a wall and wandered around the grounds of Buckingham Palace while Queen Elizabeth II was at home, British prosecutors said Friday.
Dennis Hennessy, 41, pleaded guilty to trespass during an appearance Friday at Westminster Magistrates' Court in London.
He was arrested in the palace grounds on Wednesday evening. Police said he was not armed and claimed security measures had "worked effectively."
Prosecutor Tom Nicholson told the court that Hennessy walked around the gardens for about 10 minutes toward the palace before being arrested. As he was detained just before 9 p.m., he asked "Is Ma'am in?" - a courtesy term used for the queen.
In a police interview, he said he had "walked through the gardens admiring the view."
Nicholson said the intrusion triggered a police sweep with dogs and a helicopter and caused the royal family "significant inconvenience."
The prosecutor said Hennessy had killed a homeless man in 1992, when he was 17, by hitting him with an iron bar, "fracturing his skull into small pieces," and then jumping on his head. He was convicted of murder in 1993 and released from prison on parole in 2002.
Defense lawyer Sikander Choudry said Hennessy, an unemployed stonemason, had been drinking before the palace break-in. He said Hennessy decided to scale the palace wall but "did not have any malicious intent towards the royal family."
But Judge Howard Riddle said "we simply don't know why he was there, and that makes it a matter of considerable concern."
Riddle sentenced Hennessy to four months in prison for trespassing and two months, to run concurrently, for damaging an alarm system.
Several intruders have breached security at the queen's London residence over the years - including a naked paraglider who landed on the roof in 1994.
In 2013, two men were arrested on suspicion of burglary - one in the grounds and one inside an area of the palace that's open to the public during the day.
In 1982, an unemployed man named Michael Fagan managed to climb up a drainpipe and sneak into the queen's private chambers while she was still in bed. Elizabeth spent 10 minutes chatting with him before calling for help when he asked for a cigarette.