New Delhi: At least four people were injured when a 38-year-old man on Sunday allegedly set his house on fire to kill himself and his family members, police said. The bizarre incident, which occurred in south Delhi's Jaitpur area on Sunday morning, came to light when the neighbours raised the alarm of fire. A senior police officer told IANS that Kenai Ram Mondal set the house on fire while his wife Sharmila Mondal 32, his 12-year-old son and a 62-year-old relative were asleep. All the injured were immediately taken to hospital. Mondal's son is in critical condition as he received 70 per cent burns. While Mondal sustained 15 per cent burn injuries, his wife and relative sustained 40 per cent burn injuries. A police officer said that motive for taking such extreme step is yet to be ascertained. Investigation into the matter is going on, police added.