MORRIS PLAINS, N.J. — The recent hung jury in the bribery trial of Democratic U.S. Sen. Bob Menendez shouldn’t have been a surprise, given the nature of the charges and the evidence against him, New Jersey Gov. Chris Christie said Monday.

The Republican governor, who as a U.S. attorney in New Jersey from 2002 to 2008 earned numerous convictions in official corruption cases, said Monday it’s difficult to get a conviction in a bribery case without testimony from a participant or audio or video evidence of a transaction.

“In bribery cases, if you don’t have a narrator and you don’t have tape, they become much more difficult to prove,” Christie said at a groundbreaking for a road that will bear his name. “They’re not impossible to prove, but they’re more difficult to prove. What you’re asking the jury to do then is to take circumstantial evidence and to draw certain conclusions beyond a reasonable doubt.”

A judge declared a mistrial last week after jurors failed to reach a verdict during seven days of deliberations. Jurors interviewed after the trial said the panel was strongly in favor of acquittal, with a few holdouts.

Menendez and Florida eye doctor Salomon Melgen, his longtime friend and political donor, faced multiple bribery and fraud counts. Menendez was charged with taking gifts from Melgen, including flights on a private jet and luxury vacations, in exchange for using his political influence to help Melgen in Washington.

The government’s case was built around emails between Menendez and his staffers and accounts of meetings Menendez had with government officials, allegedly to help Melgen in an $8.9 million Medicare billing dispute and other matters. Some jurors later said the case lacked a “smoking gun” that proved there was a bribery arrangement.

Christie’s most celebrated case, dubbed Bid Rig, used admitted real estate Ponzi schemer Solomon Dwek as a cooperating witness to earn guilty pleas against dozens of people, including local politicians and rabbis, who had engaged in money laundering. However, several defendants had their cases thrown out, and two were acquitted at trial.

The Department of Justice hasn’t said whether it will retry Menendez and Melgen. Christie said a hung jury doesn’t necessarily signal the government will throw in the towel.

“My view always has been … if you felt strongly about trying it once, you should probably feel strongly about trying it a second time,” he said. “But that’s something the folks at Justice will make their decision on, based on the evidence they have and how they want to proceed.”