"Six years is a long time and I'm sure he wishes it had happened years ago," Cullen said of the conclusion of the investigation. Cullen added that "for me, the result trumps the timing."
Justice Department spokeswoman Laura Sweeney declined to comment, which is normally the case when the department ends a criminal probe without filing charges.
Separately, DeLay has been indicted in Texas on charges of money laundering and conspiracy allegedly connected to 2002 state legislative elections. That case is pending.
Politico.com first reported on the closing of the U.S. Justice Department's probe of DeLay.
Last year, DeLay, a Republican from Texas, competed on ABC's hit show "Dancing With the Stars." DeLay withdrew from the ABC dance-off in October after being diagnosed with stress fractures in both feet.
Abramoff was released from a minimum-security prison camp in June.
The ex-lobbyist served about 3 1/2 years in prison for fraud, corruption and conspiracy. He spent three days in a halfway house in Baltimore before he was placed in home confinement. Abramoff currently is working in a kosher pizzeria in northwest Baltimore.