Thomas Markle Sr, 82, is under investigation after his son, Thomas Markle Jr handed over four large boxes of possessions to police in Cebu City, where the pair had been living.
Authorities are examining electronic devices allegedly containing hundreds or thousands of abusive images, with investigators seeking to establish who downloaded or possessed the files and identify any potential victims.
Thomas Markle Sr has denied all allegations against him and has not been charged.
Philippine National Police spokesperson Colonel Allen Rae Co briefed media on the investigation after the final items were surrendered.
"We are very saddened by this, and we will not let anybody, whether foreign national or Filipino national, do this to our children," he said.
"We have to establish the file and its nature, the origin of the files as well as ownership of these materials."
"If there will be evidence found of any wrongdoing, we will have to establish possession during the relevant timeline, as well as the identities of the victims if there are any," he said.
The Philippine National Police said an initial forensic examination of the material could take a week, although the quantity of evidence may mean the investigation continues for considerably longer.
According to The Sun, Thomas Markle Jr submitted a sworn statement to prosecutors before returning to provide a supplementary affidavit authorising cybercrime specialists to inspect the material.
The former window fitter said he was determined to help the investigation after discovering what he alleged were disturbing images among his father's possessions.
"It took nine hours to sign all the documentation as I handed over all that stuff but I was relieved to get it off my hands," he told The Sun.
"I think it will take months to check all these items and confirm my father is the disgusting monster I've now disowned," he said.
The Philippines' National Bureau of Investigation director, Melvin Matibag, confirmed his organisation had been in contact with the FBI about the case.
Authorities are examining whether any alleged offences could fall within American or Mexican jurisdiction, given Thomas Markle Sr's previous residences.
Thomas Markle Jr became his father's full-time carer after the former lighting director suffered a stroke in 2022.
The pair relocated from Mexico to Cebu City in January 2025, but Thomas Markle Sr subsequently returned to the US for medical treatment after a serious blood clot led to the amputation of his left leg.
Responding to the allegations against her father through a spokesperson, Meghan said her "thoughts are with any children who may have been harmed".
"I hope it can now be understood that ... any distance from my father, and my choice to not allow him to have contact with our children, was for one reason: to protect them."
Thomas Markle Sr has rejected the allegations against him, describing them as "sick lies".
