Mariusz Krężołek was born in Poland in 1979. He moved to the United Kingdom and began a relationship with Magdalena Łuczak in 2010. The couple resided in Coventry, England, where Krężołek assumed the role of stepfather to Łuczak's son, Daniel Pełka.

Between 2011 and 2012, Mariusz Krężołek and Magdalena Łuczak subjected four-year-old Daniel Pełka to prolonged abuse, including starvation, physical punishment, and emotional neglect. Daniel was deprived of food, leading him to scavenge from bins and steal from classmates. He was also forced to perform strenuous exercises and endured regular beatings. On March 1, 2012, after wetting himself, Daniel was severely beaten by Krężołek. Despite his deteriorating condition, no medical help was sought until March 3, when Łuczak called emergency services, reporting that Daniel was unresponsive. Paramedics arrived, but Daniel was pronounced dead shortly after.

A post-mortem examination revealed 22 injuries, including a fatal head injury, and signs of prolonged abuse and neglect. Both Krężołek and Łuczak were arrested and charged with murder and child cruelty. During their trial, evidence was presented of the systematic abuse Daniel endured, including being force-fed salt and subjected to water torture. On July 31, 2013, both were found guilty and subsequently sentenced to life imprisonment with a minimum term of 30 years.

While serving his sentence at HM Prison Full Sutton, Krężołek was found unresponsive in his cell on January 27, 2016. An investigation concluded that he had died from a heart attack. Reports indicated that Krężołek had refused medical attention due to fear of being recognized.