A D.C. Council committee approved giving itself the authority to issue subpoenas Friday in a probe of a quasi-public agency from which convicted Council member Harry Thomas Jr. diverted about $350,000 for his personal use.

The 4-0 vote of the Committee on Human Services came the same day it released a report that concluded Thomas may have been helped by staff of the Children and Youth and Investment Trust Corp. The action also came days before Thomas is scheduled to be sentenced on charges of filing a false return and of theft of $353,000 intended for youth sports. Thomas used the funds for personal expenses, including trips, a luxury Audi Q7 SUV and a Victory motorcycle.

Council member Jim Graham (D-Ward 1) said the subpoena power and the committee’s further investigation of the trust was part of “restoring philanthropic confidence in this organization.”

However, the vote drew swift, strong opposition from Mayor Vincent C. Gray and his administration, questioning whether the council would be investigating itself and pointing to probes by the U.S. Attorney’s Office, city Office of the Attorney General and D.C. Auditor, which is overseen by the council.

“In light of the fact that there are three active investigations, including one by an arm of the city council, it is inappropriate, inadvisable and counterproductive for a committee of the council to conduct an investigation,” Attorney General Irvin B. Nathan said in an interview Friday.

Gray (D) said in a statement that he “fully supports” the ongoing investigations. “But given questions about the Council’s relationship with the Trust, I believe these reviews should remain in the hands of the Attorney General and the U.S. Attorney,” he said.

Graham said he was astonished by Gray’s statement.

“Now, the mayor has become the spokesman for the U.S. Attorney’s Office? Is this the end of Home Rule, thank you, Mr. Mayor?” Graham asked in an interview. “I’m trying to do my job, uncover wrongdoing.”

He also said that the auditor’s inquiry is looking more broadly at the trust while the council’s investigation has a limited scope. “We see this as a very brief process. We’ve been doing this since last June,” Graham said. “I think we’re at the end of this; not beginning of this.”

Graham said he did not believe his past interactions with the trust would interfere with his ability to investigate.

Several council members, including Graham, have been involved in consulting the trust in tailoring grants to organizations within their wards or to benefit their constituencies.

But Graham said he was never accused of wrongdoing.

During the committee meeting Friday, other council members said they were supportive, but they also questioned the necessity of subpoena power.

Council member Marion Barry (D-Ward 8), who was censured and stripped of his committee in 2010 after an independent probe approved by the council, said he does not want a replay of past council investigations. “I’ve got some assurance from you that it’s not your nature to bludgeon someone with a subpoena,” Barry told Graham at the meeting.