SAN FRANCISCO (AP) — One of the biggest questions surrounding Jaycee Dugard’s kidnapping is how her alleged captor managed to keep her hidden from authorities for 18 years even as he was being monitored by parole officers because of a previous rape conviction.

On Wednesday, the California inspector general planned to release the results of a two-month inquiry into the handling of Phillip Garrido’s case.

The office has said its report would include findings from the investigation and recommendations for improving parolee supervision statewide.

Garrido, 58, was under federal parole supervision and required to register as a sex offender when he and his wife, Nancy Garrido, allegedly snatched Dugard outside her South Lake Tahoe home in 1991. Phillip Garrido had been convicted in 1977 for kidnapping and raping a 25-year-old woman.

California took over Garrido’s supervision in 1999.

As a parolee, Garrido wore a GPS-linked ankle bracelet that tracked his every movement, met with his parole agent several times each month and was subject to routine surprise home visits and random drug and alcohol tests, according to the Department of Corrections and Rehabilitation.

Still, the backyard encampment where Garrido allegedly hid and raped Dugard went unnoticed by authorities. Police say Garrido fathered Dugard’s two daughters, now 15 and 11, who were born in the ramshackle tent compound.

The Garridos have pleaded not guilty to 29 counts related to Dugard’s abduction, rape and imprisonment.

Dugard, 29, was reunited with her family in August, and is living with her daughters and mother in an undisclosed location in Northern California.