Detectives probing assassination claims by Ethics and Anti-Corruption Commission Boss Philip Kinisu have poked holes into the matter.
A bullet found at a building owned by EACC chairman Philip Kinisu in February had rusted, implying it had been there for a long time or had not been properly stored.
The report also shows that the bullet could have been fired from a pistol, contrary to earlier reports that it was from a "high-calibre rifle".
Speaking on Tuesday while responding to corruption allegations against him, Mr Kinisu claimed that there was an attempt on his life.
"A high-calibre gun fitted with a silencer was fired into my private office from a distance of 300 metres,” Kinisu said.
Experts, however, said the 9x19mm calibre bullet can only fire effectively within 50 metres.
It could also not be linked to any known past cases of shooting, said the report.
Contrary to reports that the bullet was aimed at the EACC boss, detectives said the office was then under construction and had not been occupied.
In February this year, Evans Mbugua, an agent at Kose Heights, a building owned by Mr Kinisu, reported to police that he had noticed a broken window on the fifth floor. He then saw on the floor a metallic object suspected to be a bullet head.
Mr Kinisu is facing allegations of involvement in the National Youth Service (NYS) scandal. The anti-graft boss has been accused of fraudulently pocketing Sh35 Million through his company Esaki Limited.
Kinisu has blamed corruption cartels for the criminal investigations launched against him stating that the allegations are meant to distort the truth and intimidate him.