Martin Short was concerned after he hadn’t heard from his daughter in over 24 hours, so much so that he called a friend to ask them to check on Katherine … and then she was found dead.

The Los Angeles County Medical Examiner just released Katherine’s autopsy and it reveals how Martin helped police track her down after she went MIA … only to find her with a self-inflicted gunshot wound to the head.

In the autopsy, obtained by TMZ, investigators say Martin asked a friend to go to Katherine’s Los Angeles home, where they found a note on the bedroom door, which was locked.

The friend called 911 and cops made a forced entry into her bedroom … inside they found Katherine dead in bed with a Glock 19 9mm pistol under her chest.

As we reported … a suicide note was recovered.

The autopsy says Katherine had a prior suicide attempt in 2017 involving pills … and she had a documented history of depression and other mental illnesses.

Katherine, the eldest child of Martin Short and Nancy Dolman, was only 42.