Casto was suspended Tuesday for a violation of team rules.
According to The Associated Press, Pullman, Wash., police said officers on foot patrol early Tuesday morning looked in a window of an apartment and saw someone rolling what appeared to be a marijuana cigarette. Police said they knocked on the door and police could smell marijuana when Casto answered.
Casto was cited for possession of less than 40 grams, a misdemeanor that generally results in a $250 fine and one day in jail.
"There has been a great deal of discussion regarding DeAngelo and his situation over the past 24 hours," athletic director Bill Moos said in a statement. "In reviewing new information that has been brought to my attention, I am removing DeAngelo's suspension effective immediately and he will be available to participate in tonight's NIT quarterfinal game. There are unique circumstances involving this matter and I feel the appropriate avenue to take is to allow the legal system to run its course before we consider further action."
Casto pleaded not guilty Wednesday in Whitman County District Court.
"We appreciate that [Moos] is going to allow everything to be looked at," said Tim Esser, attorney for Casto, who has predicted the case will be dismissed.
"I am disappointed in DeAngelo as he let himself and his teammates down," coach Ken Bone said in a Tuesday statement. "Neither myself nor the team will have further comment as our sole focus is the game against Northwestern and the opportunity to reach the NIT semifinals in New York."
"It is important that our student-athletes realize that they are held to a high standard and that a lack of good judgment can be costly, especially in the postseason when so much is at stake," athletic director Bill Moos said Tuesday.
The 6-foot-8 Casto averages 12.1 points and a team-leading 6.8 rebounds. Bone told 710 ESPN Seattle last week that the all-Pac-10 second team performer was considering forgoing his senior season and turning pro.
"It would be helpful if DeAngelo is back, and I'm not positive on that," Bone said, noting that Casto has a child to support. "There's a chance he won't be around. We're hoping he is. We think he will be, but it's not a for sure thing."
Diamond Leung covers college basketball for ESPN.com and can be reached at firstname.lastname@example.org. Information from The Associated Press was used in this report.