Texas A&M Student's Family Still Doesn't Believe Suicide Ruling, Attorney Says

The Austin Police Department has closed the book on Brianna Aguilera's death, ruling it a suicide ... but the family still doesn't believe law enforcement.

Tony Buzbee, the attorney for Aguilera's family, tells TMZ they still think Brianna's death was more nefarious ... adding, "The Austin Police screwed things up royally."

Buzbee says there's no credible evidence to back APD's suicide claim, full stop.

ICYMI ... Aguilera was found dead outside an apartment building on Saturday, hours after attending Texas A&M's football game against the University of Texas with trauma from an apparent fall from a high floor.

Brianna lost her phone earlier in the day, cops say ... and, she borrowed a friend's to call her boyfriend around 12:43 AM. The call lasted only about a minute -- and, then cops say Aguilera lept to her death from the 17th floor of an apartment building.

Police immediately started investigating ... and, after locating her phone, officers say they discovered a typed-out suicide note written several days before Aguilera passed away.

Stephanie Rodriguez -- Brianna's mother -- called BS on the suicide ruling in the immediate aftermath ... claiming her daughter was excited about her career in law, and insisting she wasn't suicidal.

However, Detective Robert Marshall of APD said in a press conference, "Brianna had made suicidal comments previously to friends, back in October of this year. This continued through the evening of her death, with some self-harming actions early in the evening and a text message to another friend indicating the thought of suicide."