The parents of a Southern Methodist University student who died on campus after a drug overdose question whether campus police fully investigated the case, including leads from his cellphone that they say point to a suspect.

Jacob Stiles' father said text messages indicate one of his son's Sigma Alpha Epsilon fraternity brothers provided him with drugs the night before a narcotic and alcohol mix killed the 20-year-old in December.

"We want something to happen with this investigation, and we want the truth to come out," said Tom Stiles, Jacob Stiles' father. "One of the messages clearly states there was 'snow' [cocaine] use at the house and three different brothers involved in that back-and-forth messaging."

Mr. Stiles would not give the exact wording of the text messages, which were still on his son's phone when SMU police returned it to him in January. But he said that he believes the text messages could lead police to the person who gave Jacob Stiles the drugs.

SMU Police Chief Rick Shafer said his officers followed every lead until they were all exhausted, including ones from the cellphone. But none of the information led to a suspect.

There was a conversation about drugs on the phone, Chief Shafer said, but no indication that the other student provided the drugs. There was no proof that any of the SAE fraternity members were involved in Mr. Stiles' death, he said.

Police interviewed four witnesses who said they knew Mr. Stiles used drugs and thought he bought them on Greenville Avenue in Old East Dallas. But they never saw him purchase any drugs, Chief Shafer said.

"If new leads are developed or new information is received, the case will be re-investigated to the fullest," said Chief Shafer.

The Dallas County medical examiner found cocaine, alcohol and a synthetic opiate, fentanyl, in Jacob Stiles' system. Fentanyl can be prescribed as a pain medication for cancer patients.

The sophomore from Naperville, Ill., who was studying economics, was discovered unconscious in his room at the Sigma Alpha Epsilon fraternity house about 1:30 p.m. Dec. 2. He died the same day. Someone told his parents that he had been snoring earlier that morning.

Tom Stiles said the text messages on his son's phone also indicate that he did not know what he was taking, because he referred to a different drug name than the fentanyl found in his system.

"We accept the fact that Jacob made the wrong and unfortunate choice to take these drugs," Tom Stiles wrote in an e-mailed news release. "However, we don't understand why SMU has not aggressively investigated the case and has not been forthcoming with the media and our family."

Tom Stiles said he has learned that his son's fraternity brothers regularly used drugs and that hazing was part of the SAE fraternity initiation process. In fact, it was common for pledges' drinks to randomly be drugged, he said.

No one with SAE's national office in Chicago could be reached for comment Friday.

The SMU chapter of SAE presently has 91 active members and has never been suspended from campus for any violation, according to SMU spokeswoman Patti LaSalle.

"We remain saddened by the loss of Jacob Stiles ... and the understandable grief of his family," Ms. LaSalle said. "Again, we express our sympathies and will do what we can to address with the family any issues that may require clarification."

Tom Stiles said university police have not returned repeated phone calls from his family and their attorney. The last time they talked to the campus police was four or five months ago, he said.

Since Mr. Stiles' death, two other SMU students have died from excessive drug or alcohol use.

On May 2, freshman Jordan Crist, 19, was found unconscious in a dorm room and later died. His death was ruled alcohol poisoning. He was also from Illinois.

On May 14, Meghan Bosch, a 21-year-old senior from McKinney, was found dead near a construction site near Waco. She died from an accidental overdose of cocaine, methamphetamine and oxycodone, an addictive painkiller.