The Rev. Jesse Jackson and U.S. Education Secretary Arne Duncan are among the many people mourning the apparent suicide of Chicago education chief Michael Scott, whose body was found Monday in the Chicago River.

Saying he was "shocked and saddened by the sudden death" of his "friend and colleague,” Duncan told CNN that Scott “cared passionately about public education and made many courageous decisions as president of the board. He gave his time, energy and talents to improving the life chances of children.”

"Chicago has lost a great leader, and the city's school children have lost a devoted champion," said Duncan, who served as CEO of the Chicago School Board from 2001 to 2008.

Civil rights leader Jackson, a longtime activist for Chicago schools, said he was “shocked” to learn of the death of Scott, whom he has know for the past three decades.

"Michael was so effervescent, so full of life," he told CNN.

Although a medical examiner has ruled Scott’s death a suicide, authorities say they are still investigating. According to Police Superintendent Jody Weis, Scott was found with a gunshot wound to the head.

Scott's family had reported him missing about midnight, and his body was found about 3:20 a.m., Weis said. He was last seen about 6:30 p.m. Sunday, Weis said, but he would not disclose where, saying that may be part of the investigation.

Scott's wife told police that it was "very unusual" for him not to be home by midnight, Weis said.

The gunshot entrance wound was on the left side of his head, police said. A weapon was found either under or alongside his body, Weis said, and Scott's car was in the immediate area.

CNN reports that the police investigation will include ballistics evidence and analysis of surveillance cameras in the area. It is too early for police to draw conclusions, Weiss told the news network.

"Mr. Scott was a strong advocate for education," Cook County Board President Todd Stroger said in a written statement. "His contributions to the minority communities of Cook County will be sorely missed, in particular, his love for the upward mobility of residents from Chicago's West Side, where he spent his life."

Scott had been appointed to the Chicago Board of Education three times, twice as president, CNN reports. He most recently was appointed in February. Previously, Scott was board president for five years, until July 2006.

Scott disclosed in early August that he had been subpoenaed to testify before a federal grand jury investigating how students were chosen for admission to some of Chicago's most elite public schools, CNN reports. He denied using his influence during two stints as board president to help any student into a selective-enrollment school.