The simple answer - yes. We know this from (1) Similar criminal cases (2) Published scientific literature (3) Real world settings where DNA removal/ degradation is critical.

Similar cases where no DNA/blood forensics was recovered:

Claudia Maupin and Oliver Northup - were stabbed in their bed, mutilated, disembowelled and dismembered by 15 year old school-boy Daniel Marsh. Marsh left no DNA, blood or shoe prints at the scene (he used mask, gloves and taped his shoes to avoid shoe prints) nor was any victim DNA found at his home, on his clothes or person, despite the severe mutilation of bodies which included removal of organs and insertion of foreign objects into chest cavities.

Robert Wone - was fatally stabbed, losing two thirds of his total blood volume inside a house. Police sealed the scene within 45 minutes but no blood or DNA was found other than a spot on a bed police thought his body was staged on. The 3 male residents of the house appeared freshly showered when police and paramedics arrived.

Samantha Koenig - was murdered by serial killer Israel Keyes. She was sexually assaulted and killed in his garden shed. Her body was kept in the shed for over 2 weeks and mutilated, dismembered and then transported to a lake. Keyes boasted that the FBI would find no DNA - and no DNA or blood was found in his shed or the car used to abduct her and then move her body.

Michaela McAreavey - was assaulted, strangled and dumped in a bath in her hotel room in Mauritius. Despite the scene being discovered within an hour no DNA from her attacker was recovered from her body or the room.

There are many other similar cases where killers successfully washed away all DNA traces in short periods of time and of course many cases where killers have not been apprehended in part because of successful DNA evidence cleaning.

If a 15 year old school-boy can stab and mutilate two bodies but leave no DNA evidence at the scene or in his home, and if DNA from bloody stabbings and assaults can be completely washed away within an hour beyond forensic detection, it is obvious that a car where no one was killed can be cleaned to remove forensically usable DNA over 7 weeks.

Washing away/ degrading DNA - the published science:

Washing away or degrading DNA beyond forensic use is much easier than many assume. A brief recap from previous posts (with published studies linked):

• Washing with water alone is sufficient to fully remove DNA from many smooth surfaces
• Washing once with simple dish soap is sufficient to remove all DNA from knives
• Washing carpet with hydrogen peroxide >3% destroys DNA. (Peroxide is commonly sold at c. 10%)
• Household cleaners with "active oxygen" (peroxide source) destroy blood and prevent it reacting with forensic reagents
• Peroxide is used in "color safe" laundry and fabric cleaners that do not leave bleach marks
• Hydrogen peroxide decomposes to just oxygen and water - forensically undetectable

In various laboratory settings, such as forensics or biomedical research, removal of DNA contamination on surfaces is crucial. Products are sold, based on common cleaning reagents like peroxide, which destroy DNA in minutes in a single application. There are even DNA Removal Wet Wipes available on Amazon.

Various products degrade DNA quickly and effectively, leaving no analytical trace