"He really set the standard for working across party lines and we're going to miss that," said Casey, who said Specter had helped smooth his transition when he arrived in Washington.
Anthony J. Scirica, a judge on the 3rd U.S. Circuit Court of Appeals, called Specter "irreplaceable."
"He touched so many lives," Scirica said. "He had some tough times, but he always thought that he was working for the public good."
Two of Specter's granddaughters also spoke, including Silvi Specter, a freshman at Penn who drew applause when she said she hopes to follow her grandfather into law and the U.S. Senate — before becoming president.
Shanin Specter, a prominent Philadelphia lawyer, compared his father to the fictional character Forrest Gump, given Specter's proximity to so many seminal events in modern American history.
Specter served as counsel to the Warren Commission investigating President John F Kennedy's death. He won his Senate seat in the Reagan landslide of 1980 and, as one of the Senate's sharpest legal minds, took part in 14 Supreme Court confirmation hearings.
He grilled Anita Hill when the law professor raised sexual harassment complaints against then-Supreme Court nominee Clarence Thomas. That cost him some of the support he enjoyed from female voters, but, much like the stimulus vote, he felt it was the right thing to do, former Democratic Gov. Ed Rendell recalled.
All the while, Specter fought two earlier bouts with Hodgkin lymphoma, and overcame a brain tumor and cardiac arrest following bypass surgery. He then announced in August that he was again battling cancer.
"There are some things that even the most robust human spirit can't conquer," said Rendell, choking up.
His greatest legacy, his friends said, may be the $10 million in federal money he steered into cancer research.
Specter is also survived by his wife, Joan, son Steve and three other granddaughters.