CHICAGO (AFP) - A United States police officer whose death prompted a massive manhunt "carefully staged" his suicide to make it look like murder, officials said on Wednesday (Nov 4).

His death on Sept 1 came as the country was reeling from a series of what appeared to be targeted shootings of police officers amidst heightened tensions following the deaths of a number of unarmed black men at the hands of police.

Lieutenant Charles Joseph Gliniewicz radioed in that he was pursuing three men on foot and then called for backup a few minutes later. Hundreds of officers fruitlessly searched for the suspects after his body was discovered in the woods near the town of Fox Lake, Illinois.

Officers from more than 1,000 police forces reportedly attended his funeral, where he was memorialised as a hero.

"We have determined this staged suicide was the end result of extensive criminal acts that Gliniewicz had been committing," Mr George Filenko, commander of Lake County major crime task force, told reporters.

"Gliniewicz committed the ultimate betrayal to the citizens he served and the entire law enforcement community." Some 150 officers spent over 25,000 hours investigating the case.

They found that Gliniewicz had been stealing from the department for seven years, diverting funds from a programme aimed at encouraging young people to become police officers.

He had gained a significant amount of experience in staging mock crime scenes while running the programme and used that to try to fool investigators.

He left a "staged train of police equipment" at the scene and then fired the first shot into his bullet proof vest, before lifting the vest to fire the second, fatal, shot.

His ruse began to unravel, however, after investigators saw no signs that he had fought for his life, or that his body was dragged after the initial shot, Mr Filenko said.