Prosecutors in South Korea have demanded a 12-year prison sentence for the acting head of Samsung over his alleged role in a bribery and corruption scandal that toppled the country’s former president Park Geun-hye.

Speaking at the final hearing in his four-month trial at Seoul central district court on Monday, Lee Jae-yong fought back tears as he denied trying to seek political favours from Park in exchange for making large donations to foundations run by her close friend and confidante Choi Soon-sil.

Lee is officially Samsung’s vice-president but has in effect run the company since his father, Lee Kun-hee, had a heart attack in 2014. He was arrested in February on charges of bribery, embezzlement and perjury.

The billionaire scion of South Korea’s richest family told the court: “I have never asked anyone, including the president, for anything for the company or my personal gain.”

After pausing and sipping water to regain his composure, he added: “I deeply regret that I have given such disappointment and apologise.”

He described his arrest and trial as “unjust” but added that he had the chance to reflect on his conduct during his six months in jail and accepted that the more Samsung had grown, “the stricter and higher the expectations from the public and society”.

But he added: “Whether it was for my personal profit or for myself, I have never asked the president for any favours.”

Prosecutors said Samsung’s alleged involvement in the Park scandal was indicative of the collusive ties between South Korea’s government and powerful, family-controlled conglomerates – or chaebol – of which Samsung is the largest.

The special prosecutor, Park Young-soo, accused Samsung executives of lying in their testimony to protect Lee, who faces the longest prison term for any South Korean executive if convicted.

Samsung, whose group revenues are equivalent to almost a fifth of South Korea’s GDP, did not comment on the prosecutors’ demand. The court will deliver its verdict on 25 August.

Park Geun-hye outside court in Seoul on Monday. Photograph: Ahn Young-joon/AP

Prosecutors allege that Lee was the ultimate beneficiary of a range of crimes that involved four other Samsung executives, including Choi Gee-sung, the former head of its corporate strategy office, who faces 10 years in prison.

Lee allegedly offered $38m (£29m) in bribes to four entities controlled by Choi, to whom Park often turned for advice on policy, such as the security threat from North Korea.

Samsung was the biggest single donor to the foundations, which Choi had set up to support Park’s policy initiatives. Samsung has not denied donating money to the organisations, but said it was coerced to do so by Park.

The company is also accused of separately giving Choi millions of euros to fund her daughter’s equestrian training in Germany. In return, Lee allegedly sought government approval for the contentious $8bn merger of two Samsung affiliates in 2015 – a move that would cement his control of the business empire.

The merger was opposed by many shareholders, but went through after the national pension fund – a major Samsung shareholder – approved it.

“Even though Lee is the ultimate beneficiary, he has been pushing the blame on others [who have been] accused,” Park, the prosecutor, told the court.

Lee has insisted he played no part in decisions concerning the wider Samsung group and “mostly listened to other executives”. His lawyers said prosecutors had failed to provide any evidence of attempts by Lee to manipulate the succession process at Samsung.

Park Geun-hye, who became South Korea’s first female president in 2012, is standing trial separately on a raft of charges including bribery, coercion and abuse of power following her dismissal from office in March.

Park, who faces a possible life sentence, was formally impeached after public uproar over her questionable ties with Choi sparked months of mass protests.

