In the constantly evolving field of cybersecurity, it is imperative for analysts to stay abreast of the latest attack trends and pertinent information that aids in the investigation and attribution of cyber-attacks. In this work, we introduce the first question-answering (QA) model and its application that provides information to the cybersecurity experts about cyber-attacks investigations and attribution. Our QA model is based on Retrieval Augmented Generation (RAG) techniques together with a Large Language Model (LLM) and provides answers to the users' queries based on either our knowledge base (KB) that contains curated information about cyber-attacks investigations and attribution or on outside resources provided by the users. We have tested and evaluated our QA model with various types of questions, including KB-based, metadata-based, specific documents from the KB, and external sources-based questions. We compared the answers for KB-based questions with those from OpenAI's GPT-3.5 and the latest GPT-4o LLMs. Our proposed QA model outperforms OpenAI's GPT models by providing the source of the answers and overcoming the hallucination limitations of the GPT models, which is critical for cyber-attack investigation and attribution. Additionally, our analysis showed that when the RAG QA model is given few-shot examples rather than zero-shot instructions, it generates better answers compared to cases where no examples are supplied in addition to the query.