12:10 PM PT -- Matt Barnes tells TMZ Sports ... "We are so grateful to everyone who helped us -- from spreading the word thru social media to calling the Sacremento PD with your citizen tips."
He adds, "It was a citizen tip that led police to Michael Williams' very location late this morning. Thank you again for allowing me to be my auntie's voice and to help bring this suspect in. Also, thank you to the Sac PD!"
The man suspected of murdering Matt Barnes' aunt has been CAPTURED by police in Sacramento ... and officials say it's all thanks to a concerned citizen who tipped off the cops.
As we previously reported, the L.A. Clippers star went to social media and begged his fans to be on the lookout for Michael Williams -- the estranged ex-husband of the victim.
Cops believe Williams is a transient and the victim (Matt's aunt) was going to visit him when he snapped and stabbed her to death on the streets of Sacramento on July 8th.
Now, the Sacramento PD has confirmed ... "Michael Williams, suspect in the 24th street homicide, is in police custody thanks to a citizen tip. He was located in the Sacramento area."