CORONADO, Calif. (CBS 8) - The millionaire boyfriend of Rebecca Zahau will allow her family's attorneys to launch a new investigation inside the Spreckels mansion before the end of the year.

Earlier this month, attorneys Anne Bremner and Marty Rudoy wrote a letter on behalf of the Zahau family to the mansion's owner, Arizona pharmaceutical tycoon Jonah Shacknai, and requested access to the historic mansion in Coronado.

The attorneys want to investigate the death of Zahau, 32, which occurred at the oceanfront home on July 13; and photograph, videotape, measure and "recreate what actually happened to see whether it matches what the Sheriff believes may have happened," according to Rudoy.

"We're interested in the bed, the bed movement, the configuration of the ropes that may have been used and the condition of the balcony; how the balcony may have been involved in the incident and the yard," said Rudoy during a telephone interview from his office in Los Angeles.

Bremner and Rudoy received a written response Monday from Jonah Shacknai's Chicago-based attorney, Daniel Webb.

Rudoy declined to release the entire letter but quoted excerpts to News 8:

"While my client has no reason to doubt the findings and conclusions of the San Diego Sheriff's Department and Coronado Police Department, my client will allow access to the property for inspection and non-destructive testing as requested," Webb wrote on behalf of Jonah Shacknai, 55.

"However, we believe this inspection and any non-destructive testing should be conducted in cooperation with – and under the supervision of – the Sheriff's department so that there will be no problem or interference with law enforcement should they decide to do any further review of the matter," the letter continued.

In September, Sheriff's detectives and the San Diego County Medical Examiner ruled Zahau's death a suicide by hanging. Zahau's family members have voiced strong opposition to the suicide finding, and openly expressed their distrust of the Sheriff's department in national media interviews.

Zahau's sister, Mary Zahau-Loehner, 34, appeared on the Dr. Phil Show and told the talk show host she believed her sister was murdered.

San Diego Sheriff Bill Gore has said his department might be willing to re-open the case if relevant, new evidence came to light.

"There's some forensic testing that we want to do," said attorney Rudoy. "We want to see if it's even possible for Rebecca to have committed suicide, which we doubt."

Shacknai's response letter did set some ground rules in exchange for access to the mansion.

"We would also request that you provide us copies of any test results or reports that are generated as a result of the inspection and non-destructive testing," Webb's letter read.

The Spreckels mansion currently is in escrow under the terms of a private, real estate contract signed between Shacknai and an investment group, which plans to remodel the estate. The Ocean Blvd. home is on the market for $14.5 million.

In his response letter, Shacknai's attorney spelled out a timeline for the new investigation to be concluded.

"As noted, my client has recently sold the property. The new owner is scheduled to take possession and begin renovation of the property on January 1, 2012. Accordingly, you need to undertake and complete your inspection prior to January 1, 2012," the letter said.

"As we expect that you will contact the Sheriff's department to move forward with any inspection, I will advise the Sheriff that my client consents to the procedure," attorney Webb wrote.

Rudoy said an email has been sent to Sheriff Gore requesting his department's assistance with the inspection of the mansion. The Sheriff's department has not announced whether it will get involved.

"We believe the Sheriff's department has an interest in serving its citizenry in cooperating with both Mr. Shacknai and our request that the Sheriff be involved," said Rudoy. "The clock is ticking. We only have 18 days until the new owners take over. Any delay on the part of the Sheriff would prejudice my clients' rights."

Rudoy said his investigators will also review the circumstances surrounding the death of Shacknai's 6-year-old son, Max Shacknai, after the boy suffered a fall down the mansion staircase July 11.

"While it's not the primary focus of our investigations, we do wish to look at that circumstance as well," said Rudoy.

The attorney believes the decor inside the home essentially remains intact and a forensic review of the property could reveal new evidence in the case.

"My understanding is that the furniture and fixtures are still in place. The carpets and rugs apparently are still in place," said Rudoy. "We have asked Mr. Shacknai's attorneys to not make any changes between now and our date of testing so that we can keep the condition of the premises, inside and out, as close to the condition it was in as of the date of the death."

"In my opinion, there shouldn't be any ground rules as long as we don't disturb or alter the property," Rudoy continued. "If there were a lawsuit we would be entitled to do this and so I think Jonah's attorneys are being smart in approving it."