But whatever their findings, Park will not be charged due to a law that makes the president immune from prosecution.
South Korean prosecutors announced Sunday there was enough evidence charge Choi Soon-sil, a friend of the president, and former aides An Chong-bum and Chung Ho-sung.
Lee Young-ryol, the prosecutor who led the corruption probe, said Choi and An are being charged with abuse of power, fraud and coercion. Chung faces charges related to leaking classified documents to Choi through email, phone and fax.
"Park cannot be charged with any 'crime' as a sitting president in accordance with Korean constitution but prosecutors will continue to investigate Park Geun-hye," Lee said.
Park will become the nation's first sitting president to be investigated as a suspect, CNN's Paula Hancocks said.
According to the South Korean constitution, the president cannot be charged with a crime while holding office except for insurrection or treason.
A spokesperson for the Blue House blasted the investigation as one that has "ignored fairness."
"Her rights of getting a fair chance of due legal process has been taken away," the Blue House spokesperson said.
Choi charged following arrest
The presidential scandal first started
when CNN South Korean affiliate JTBC found evidence that Choi had received secret documents on an abandoned tablet device.
When Choi's father died, she succeeded him as leader of the Eternal Life Church. For years, she has given Park spiritual guidance.
"It's much more than simply, 'Oh she knows this person,' it's deeply intertwined, almost like they're Rasputin and Park Geun-hye is just a puppet," David Kang, director of the Korean Studies Institute at the University of Southern California, recently told
Choi, who was arrested in early November, faced accusations that she used her relationship with Park to acquire millions of dollars in donations for her foundations.
Prior to her arrest, Choi had issued an apology and said that she had "committed a deadly sin," according to CNN affiliate YTN.
"My apologies to the public," she said at the time. "Please forgive me."
Park has apologized multiple times for her role in the scandal.
Multiple aides, multiple resignations
Park has ordered the resignation of 10 of her senior secretaries -- aides who coordinate policy -- as political turmoil gripped the country.
Multiple aides to President Park have resigned in the wake of the scandal, including four senior secretaries responsible for political affairs and policy coordination.
Park also sacked the country's prime minister Hwang Kyo-ahn, replacing him with Kim Byong-joon, a professor at Seoul's Kookmin University.
Protesters: Park should resign as president
Massive demonstrations have taken place across South Korea to demand Park's resignation, according to the country's Yonhap news agency.
Earlier this month, protesters gathered around the presidential compound in the South Korean capital of Seoul to vent their anger at President Park.
It was one of the biggest anti-government protests the country has seen in decades, according to Hancocks
Following that demonstration, Park's spokesman said the President had "heard the voices of the people yesterday with gravity and deeply realizes the seriousness of the current situation."
He added that Park was considering ways to "normalize the state of affairs and fulfill her responsibility as President."
Park spokesperson fires back
In a statement, a spokesperson from the Blue House called the prosecutor's remarks "regrettable," given the perception that the president has committed a crime.
"What the Prosecutors' office have said today is not true and that they have ignored the facts and it is only based on speculation and imagination," the spokesperson said.
Nevertheless, Park still planned to cooperate with prosecutors for questions this week to order to "prove her innocence."
During the scandal, the spokesperson noted the likelihood of the president getting a fair chance of due legal process has been taken away.