A Polish military prosecutor linked to an investigation into the 2010 air crash that killed President Lech Kaczynski shot himself in the head yesterday after abruptly cutting short a news conference where he had been defending the work of his office.

Colonel Mikolaj Przybyl was speaking to reporters and cameramen from Polish television at his office in the western city of Poznan when he suddenly asked the journalists to leave because he needed "a rest". Seconds after the journalists walked out, they heard a bang.

"We heard a loud thud and we went back into the room thinking that one of the cameras had fallen over," one of the reporters told Polish television. "Then we saw the colonel lying motionless on the floor in a pool of blood with his military issue firearm beside him."

Colonel Przybyl was immediately taken to hospital. Doctors said the shot had damaged his skull but his life was not in danger. They said they were carrying out a computer scan to assess the extent of his injuries.

At the news conference the colonel attempted to defend himself against allegations that his office had eavesdropped on journalists conducting their own investigation into the crash at an airport serving the Russian city of Smolensk. He also said he objected to plans by the Prosecutor General, Andrzej Seremet, to put military prosecutors under civilian authority.

Television footage shows the bearded, shaven-headed colonel reading out a statement to reporters. "During my entire service as a civilian and later military prosecutor, I have never brought shame to the Republic of Poland," he tells them. "I will continue to uphold the honour of an officer of the Polish armed forces. Thank you, please give me a five-minute break, I need a rest."

Colonel Przybyl then walks out of frame. The sound of a gun being cocked can be heard. It is followed by a loud bang. Subsequent pictures show shocked journalists gathered around the uniformed body of the colonel, who is slumped on the floor of his office beneath a wall-mounted Polish eagle, the official emblem of the state.

Earlier the colonel had categorically denied suggestions that military prosecutors in Poznan spied on journalists investigating the crash. An official plane carrying a delegation headed by Mr Kaczynski had been flying to Smolensk, where the party had planned to attend the 70th anniversary of the Katyn massacre of Polish officers by the Soviet secret police.

The aircraft crashed in thick fog while attempting to land. The President, his wife and the other 93 people on board were killed. Investigators finally concluded that pilot error was to blame.