A man bludgeoned his flatmate to death in Kettering with a wooden table leg, a court heard.
Lithuanian national Juozas Meilunas, 51, was found dead in a flat in Woodlands Court off Wood Street just before 6.30pm on December 26 after a leak was spotted.
He had died several weeks earlier.
Today (Tuesday) the trial of a man charged with his murder - 29-year-old Mindaugas Kaminskas - began at Northampton Crown Court.
The court heard the flat, on the first floor of a converted factory, had become so run down it was almost uninhabitable.
On Boxing Day last year neighbours living in the block noticed two young men running away from the flat, believed to be trespassers. They went to check the property and it appeared a water pipe had been damaged as it was being flooded.
They called the fire service and police, who inspected the flat without initially finding anything.
Prosecuting, Mary Loram said: "Eventually a police officer noticed that, under a duvet in a bedroom, was a body in a fairly advanced state of decomposition."
Over the next few days police established the body was Mr Meilunas, who been working for agencies in the town for several years and was part of the street drinking community.
A pathologist established he died as a result of blows to his head, probably caused by a blunt object.
Blood was found on walls above the bed Mr Meilunas was discovered in.
Mrs Loram said the blood pattern indicated he was struck when he was standing or sitting up before being hit again as he was lower down.
The prosecution's case is that fellow Lithuanian Kaminskas, of no fixed abode, battered him with a wooden table leg found near the body. Mrs Loram said Mr Meilunas had been killed in an "explosion of violence".
Mrs Loram said: "When it [the table leg] was examined it was found to have blood, skin and hairs on it.
"They matched the DNA of Juozas Meilunas and were at the foot end of it.
"At the other end there was DNA matching Juozas Meilunas and the defendant."
Further examinations of the flat found a pair of blood-stained trousers with both Mr Meilunas' and Kaminskas' DNA on.
Kaminskas had been living at the flat having previously moved in in April and then a second time in September.
Mrs Loram added: "It's not entirely clear why [he killed him] but that does not matter.
"The evidence that it was him is clear."
The trial is expected to last three weeks.