New Jersey's U.S. senators said Monday they'll continue their investigation into what role BP PLC may have played in the release of convicted Pan Am 103 bomber Abdel Baset al-Megrahi last year, and will consider issuing a subpoena to BP CEO Tony Hayward.

Sen. Robert Menendez, leading a Senate Foreign Relations Committee investigation, had scheduled a hearing on Capitol Hill last week that was canceled after BP and British and Scottish government officials declined to attend.

He and Sen. Frank Lautenberg, both Democrats, said at a news conference Monday they would continue to push the British and Scottish governments to release documents regarding al-Megrahi's release. Menendez said he plans to hold a hearing in September.

"They have stonewalled to this point, and I'm disappointed they have found it necessary to do so," Menendez said. "But we do not intend to take it lying down. This is not over."

Although he is not a committee member, Lautenberg has been working with the families of those who died in the bombing.

Al-Megrahi was convicted in 2001 of the Dec. 21, 1988, bombing that killed 270 people, including 38 from New Jersey. He was sentenced to life in prison, but Scottish Justice Secretary Kenny MacAskill decided last August to release him on compassionate grounds because the Libyan was diagnosed with terminal cancer. The decision outraged victims' families and drew criticism from U.S. officials.

"The message it sends to the terrorists of the world is, 'Do your time, and you'll be out in a few years,'" Eileen Walsh of Glen Rock, who lost three family members in the bombing, said Monday.

BP has acknowledged it lobbied the British government to sign a prisoner transfer agreement with Libya for al-Megrahi, but denied specifically seeking his release. The Senate committee is looking into whether BP sought al-Megrahi's release to help get a $900 million exploration agreement with Libya off the ground.

In a letter to Menendez dated Monday, First Minister of Scotland Alex Salmond wrote that "no one has produced any evidence" of a link between BP and the Scottish government's decision to grant al-Megrahi compassionate release "because there is none."

Salmond added that Scottish officials declined to appear at last week's hearing out of principle since they are accountable to the Scottish Parliament and not to other legislatures.

"The most appropriate way for us to assist the Foreign Relations Committee is to provide a statement of the position of the Scottish Government, as I have done, and to answer any questions that the Committee may have in writing, as we have also done," he wrote.

A spokeswoman for the British Embassy in Washington said the British government had not received any additional requests for information or assistance from the Senate committee and would consider such requests if and when they were made.

Among the documents sought by Menendez and Lautenberg are medical opinions from doctors who concluded that al-Megrahi had three months to live. Rumors have circulated that some of the doctors had been contacted by the Libyan government, Menendez said.

"We want to know about the doctors who said there were three months left, and now it's been said he could live another 10 years," Lautenberg said. "How could you get it so wrong?"

Menendez conceded Monday that the committee can't compel foreign nationals to testify at a hearing in the U.S., but said the committee would look into whether Hayward could be subpoenaed since British-based BP conducts business in the U.S. A spokesman for BP didn't immediately return phone and e-mail messages.

Both senators and the family members said they hoped the public outcry over al-Megrahi's release would serve as motivation.

"There's nothing we can do legally to go after BP, but we're hoping there's some way, somehow, that we can get them under oath so they can testify," said Montville resident Jack Flynn, whose son was on Pan Am 103. "Then they have to tell the truth."