Replies

Oswald owned the rifle,

Yes, Oswald owned the rifle found on the sixth floor of the TSDB.

However, the the US Army and FBI testified to the Warren Commission that Oswald's rifle was not in usable condition in its original state and most likely the weapon was not used in the assassination. You can read their testimony here:

Warren Commission Hearings, vol. 3, p.443.
https://www.maryferrell.org/mffweb/archive/viewer/showDoc.do?docId=39&relPageId=451

Warren Commission Hearings, vol.3, p.405.
https://www.maryferrell.org/mffweb/archive/viewer/showDoc.do?absPageId=16613

Warren Commission Hearings, vol.3, p.449.
https://www.maryferrell.org/mffweb/archive/viewer/showDoc.do?docId=39&relPageId=455

and he killed a policeman

The Warren Commission concluded that Oswald shot Officer Tippet, but neither the FBI nor the Dallas police came to that conclusion. Tippet's murder is an unsolved mystery.

The pistol that was found on Oswald when he was arrested was unserviceable (Oswald wasn't good at maintaining his weapons). The FBI laboratory stated that Oswald’s pistol was defective: “the firing pin would not strike … the cartridges with sufficient force to fire them” (Jevons to Conrad, 12 February 1964, FBI HQ JFK Assassination File, 62–109060–916).

he had built a sniper's nest next to the window, he fled the scene after the shooting

I don't have any doubts that Oswald was involved in the assassination plot. According to James Files' interview with Robert Vernon, Files stated that Oswald's duty was to "plant evidence to mislead everybody," not to shoot.

https://drtruth.fortunecity.ws/confession2.htm

Oswald was probably right, when he realized afterwards, that he was the "patsy," or fall guy, for the shooting.