NEW YORK (CNN/Money) - Arthur Andersen LLP called its last witness, John Riley, the accounting firm's in-house expert on the Securities and Exchange Commission, who testified Monday that when he visited the Houston office last year the possibility of a federal investigation into Andersen never occurred to him.

While he didn't consider the possibility of a federal investigation, Riley said he was initially concerned about paper shredding occurring at the Houston office last October.

"Well, this wouldn't be the best time in the world for you guys to be shredding a lot of stuff," Riley testified that he told David Duncan, then lead auditor on the Enron Corp. account.

Duncan claimed that he understood, but that the shredding was for "clients' confidential information and routine stuff," Riley said. Duncan on Oct. 23 held a meeting with employees where he ordered staff to comply with the firm's document retention policy, though he denies directing anyone to destroy documents.

"It sounded like it was OK to me," Riley, who worked at the SEC for 11 years, testified Monday.

Andersen in January fired Duncan for directing the shredding of Enron documents. On April 9, the former Andersen executive reached a deal with the Justice Department under which he pleaded guilty to obstruction of justice and admitted that he directed the shredding of Enron documents to thwart the government's investigation. Duncan also agreed to serve as government witness against Andersen and testified against the accounting firm in the Houston criminal trial.

Riley's testimony Monday comes as Andersen prepares to wrap its defense in the criminal trial.

The Chicago-based accounting firm is currently on trial for allegedly obstructing justice when it shredded Enron documents last year while on notice of a federal investigation. Riley is Andersen's twelfth witness as the criminal trial heads into its fifth week.

The government is expected to continue cross-examining Riley on Tuesday. Prosecutors will likely call witnesses to rebut testimony on Tuesday and closing arguments could begin Wednesday.

Earlier Monday, Shannon Adlong, Duncan's executive assistant, testified that the former Andersen partner reluctantly sifted through his files after ordering employees to comply with the accounting firm's document policy, which calls for the destruction of irrelevant documents.

"He was acting like he had to do this," Adlong said of Duncan's demeanor. "It was just the way he was walking, the way he came out of his office and said. 'OK, I'd better go through my files.' And I said, 'Yeah, you'd better because everyone else has."'

Adlong on Monday said she never heard of the firm's document policy before Duncan received a reminder of it in October. Andersen in house counsel Nancy Temple sent an Oct. 12 e-mail that was forwarded to Duncan reminding executives of the firm's guidelines.

Andersen lead defense attorney Rusty Hardin introduced two e-mails sent by an Enron audit team member, Melissa Durochez, from April 2001 and August 2002. The e-mails show that Durochez, who was lower than a partner or mid-level manager but still in a higher position than Adlong, reminded other staffers of the firm's document policy.

Adlong never received the Durochez reminders.

The accounting firm has admitted that its employees destroyed documents related to its audit of Enron, but denied the action was part of a deliberate act of wrongdoing by the firm's top decision-makers. Government lawyers claim that Andersen's sudden promotion of its document retention policy in October was an implicit effort to destroy documents in light of a Securities and Exchange Commission investigation into Enron.

Adlong on Friday sobbed during her testimony as she described Duncan, her former boss, as "considerate, encouraging and fun to be around," she said. But on cross-examination Monday Adlong gave short, emotionless and sometimes hostile replies.

Government lawyers on cross-examination pressed Adlong on statements she made to FBI agents in February. Adlong told the agents that in October she heard someone say that the Enron team had better "get its ducks in a row" because someone from outside might be interested in the files.

Prosecutor Sam Buell tried to get Adlong to say that she meant someone outside the firm, like the SEC investigators, but Adlong was steadfast that she meant personnel from the accounting firm's Chicago headquarters.

"I remember talking about someone outside, but I meant someone outside the Houston office," she said. Adlong conceded she had done so many interviews with so many people that she could not remember exactly what she said.

Buell also wanted to introduce a 200-page deposition Adlong gave in the Enron civil litigation to contradict her testimony. Judge Melinda Harmon, who is overseeing the trial, will rule later.  

--Staff and Wires