BOSTON (CBS) – Boston Mayor Tom Menino has finally picked a side in the U.S. Senate race in Massachusetts.

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WBZ NewsRadio 1030’s Lana Jones reports

Sources told WBZ NewsRadio 1030 and WBZ-TV’s Jon Keller Thursday that Menino will endorse Elizabeth Warren at a rally in Roslindale Friday.

Menino has so far refused to say who he’d support.

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The mayor, who’s a Democrat, has been friends with Republican Senator Scott Brown for years.

Menino endorsed Martha Coakley in Brown’s last race, but Keller said that support was lukewarm.

“There was clearly not much juice behind that and that matters.  A Democratic candidate running statewide has got to come roaring out of Boston with a huge vote advantage in order to propel them statewide,” Keller said.

Brown and Warren will face each other in their first debate tonight on WBZ-TV at 7 p.m.

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You can also watch it live on CBS Boston.com and listen live on WBZ NewsRadio 1030.