Prosecutors in a high-profile murder trial in the United States have presented their closing arguments, offering an account of why they believe Alex Murdaugh, a prominent figure in his South Carolina community, killed his wife and son.

Prosecutors described the deaths of Maggie Murdaugh, 52, and Paul Murdaugh, 22, as the calculated act of a desperate man looking to shift attention from his financial crimes and opioid addiction.

“As all of these pressures were mounting, the defendant killed Maggie and Paul,” lead prosecutor Creighton Waters said of Alex Murdaugh, 54.

Speaking to a jury in the Colleton County Courthouse in Walterboro, South Carolina on Wednesday, Waters alleged that Murdaugh — a now-disbarred lawyer from a powerful legal dynasty — drew on his knowledge of criminal cases to execute the crime.

Maggie and Paul Murdaugh were found shot to death near the dog kennels at the family’s rural hunting lodge on June 7, 2021. Alex Murdaugh has denied any involvement in their deaths.

Raising a mobile phone into the air during his closing arguments, Waters referenced a key piece of evidence pulled from Paul’s iPhone to paint the elder Murdaugh as a serial liar.

Federal investigators worked for more than a year to hack into the iPhone, eventually discovering it contained a video recording that captures Murdaugh’s voice near the dog kennels minutes before the phone became inactive.

Prosecutors allege that is when the double murder occurred, though Murdaugh maintains he left before the shooting took place to visit his mother, who suffers from dementia. In early interviews, Murdaugh initially denied being near the kennels on the night of the attack.

“The forensic timeline puts him there,” Waters told the jury on Wednesday. “After an exhaustive investigation, there is only one person who had the motive, who had the means, who had the opportunity to commit these crimes, and also whose guilty conduct after these crimes betrays him.”

The defence will present its closing argument on Thursday. Throughout the trial, it has sought to highlight what it considered gaps in the prosecution’s arguments and flaws in the overall investigation.

The firearms used in the shootings have never been recovered, and there is no DNA linking Murdaugh to the killings, the defence team has said. They argued investigators jumped to conclusions about their client without considering other suspects.

Throughout the trial, defence lawyers have also pointed to possible mismanagement of the crime scene, alleging a failure to properly dust for fingerprints and inadequate photography.

The victims’ bodies, for instance, were covered in a fabric sheet rather than a tarp, which could have picked up fluids or hair, the defence team explained. That the sheet was later discarded could mean evidence was lost with it, they said.

Before the prosecution’s closing arguments on Wednesday, the jury also visited the Murdaugh property to examine the crime scene, at the request of the defence.

While prosecutors objected to the visit on the grounds that the crime scene had changed since 2021, Murdaugh’s lawyers hoped the walk-through – which indicated the distance between the two victims’ bodies – would lead the jury to consider alternative theories about who perpetrated the shootings.

This week’s closing arguments culminate a nearly six-week-long murder trial against Murdaugh, which included 800 evidence exhibits and 75 witnesses, including the defendant himself.

If convicted, Murdaugh could face a sentence of between 30 years to life. Prosecutors are not seeking the death penalty in the case.

The murder trial is only part of Murdaugh’s ongoing legal woes. He has also been charged with more than 100 counts of financial crimes and other misdeeds.

Prosecutors in those cases have accused Murdaugh of stealing $7m from his family’s law firm and $8.8m in legal settlements from his clients, many of whom suffered injuries or had relatives killed in accidents.

Murdaugh was initially arrested in October 2021, on felony charges after millions in settlement funds went missing from his late housekeeper’s family.

The cases against Murdaugh have brought national scrutiny to rural South Carolina, where Murdaugh’s family has held sway for nearly a century.

Three generations of Murdaughs — the defendant’s father, grandfather and great-grandfather — have all held the elected position of solicitor for South Carolina’s 14th Circuit, which empowered them to prosecute criminal cases across five counties.

Murdaugh called emergency services at about 10:07pm on June 7, 2021, to report the death of his wife and younger son. He claimed to have found them after returning from his mother’s home.

Investigators said Maggie Murdaugh died from four to five rifle shots, while Paul Murdaugh was killed by two shotgun blasts, each with a different-sized round.

Alex Murdaugh was charged for their deaths nearly a year later, on July 14, 2022.