Brāhmanahatya, "the act of killing a Brahmin". Puranas considers this act to be a major sin, worse than "ordinary" murder. It is a serious crime which has to be faced by the guilty one and his generations in the form of a curse.

Brāhmanahatya, "the act of killing a Brahmin". Puranas considers this act to be a major sin, worse than "ordinary" murder. It is a serious crime which has to be faced by the guilty one and his generations in the form of a curse. It is not limited to the killing of a brahmin. It also means killing of all those creatures which are equivalent to brahmin. Ravana was a Brahmin, he was a highly accomplished scholar. He is described as a great scholar and a Shiva bhakta and is considered to be the author of the Shivatandava Stotram. In killing Ravana, lord Rama is said to have incurred three sins, killing a great Brahman, a great scholar and a great devotee. Lord Rama got the Brahmahatya dosham by killing Ravana. To get rid of it he installed the lingam at Rameswaram and worshipped Lord Shiva, to absolve himself of his sins. ‪There are some means to get rid of the dosham, like japa, tapa, homa, yagya, tarpan and shradh kriya. Brahma dosha nivarana pooja is also mandatory. In such cases trimbaka pooja at triyambakeshwara and pinda daan at gaya is also suggested. As per Vamana Purana, a pilgrimage to Kashi liberates one of all his sins. It's mentioned in Vamana Purana that In a fight Lord Shiva severed two of Brahmas heads. Lord Shiva had committed a grave sin of Brahmahatya. He decided to go to Badrikashrama to atone for his sins. After reaching there, he became worried when he did not find Lord Vishnu. He went to take a bath in river Yamuna but as soon as he entered the river, the water dried up. He experienced this strange phenomenon at the Saraswati River as well. He then made pilgrimages to numerous sacred and holy places but still did not become free from Brahmahatya. Dejected, he ultimately requested Lord Vishnu who advised him to go on a pilgrimage to Varanasi where he was finally liberated from his sins.  Brahman is equated with a holy cow and is revered because of his saatvik qualities and way of living. Hence killing a cow and killing a brahmin are considered sins. If a person does this, they indulge in unending birth and death cycle of all creatures and suffer. However, to overcome this Brāhmanahatya dosham, scriptures have recommended various penances. The Shiva Purana states that a person would get rid of Brahmahatya dosham just by having darshan of a round ek mukhi rudraksha. Since this is not affordable and is not available easily, natives have other choices. Shiva Purana states that if a person wears a six mukhi rudraksha, it would get rid of all doshams including Brahmahatya dosham. since six mukh rudraksha costs only a couple of hundred rupees, this remedy is easy for Brahmahatya dosham. And several puranas also mention that worshipping shaligrama shila would get rid of Brahmahatya dosham.!
Om Namah Shivaya