There was a family of 4 people . They had a daughter named Rina and his brother's name was Tarun . Everyone knew that their father was a scientist, and is on in doing some experiments all day and night and is trying to invent something , yet it was not known to them what he was trying to invent .
The family had some workers , like the maid , the cook , the watchman , etc .
Murder/Suicide $1$ :- The family lived happily for a lot of days , but one day turned out to be terrible . The daughter Rina was found dead this morning . Detective Sherlock Holmes was immediately called for the case :-
He found some evidences, and interrogated her mother who was the only one there with her and the $1$st to find her body at the kitchen .
Evidences :- Rina's body was found in the kitchen . It was clutched on the ground , with her chin touching a base of the kitchen . On her left-hand was a matchbox and on her right-hand was a matchstick which was burned out . On the stove stood a pressure cooker , which wasn't lighted up.
Interrogation :- On interrogating with her mother , she said, "I was knitting a sweater. I also thought to cook some food in a pressure cooker . When the cook is absent, I usually do the cooking, but I just thought to tell my daughter about it. So I asked my daughter to lit up the pressure cooker in the kitchen. It took a lot of time for her to return , so I thought to check her once in the kitchen, and found her dead."
On interrogating more, Sherlock found that the cook was absent that day, and the maid was cleaning another room, and the watchman was watching the outside gate, the milkman gave $3$ bottles of milk that day, and so on. His brother was watching TV and his father was sleeping in his bed.
Sherlock found the death of Rina to happen at morning. Sherlock also found out that the mother liked to smoke, and she would cook food by herself only and would smoke once every evening and before bed at night.
Sherlock didn't found out any bullet wounds , scratches , etc on her body . Also there was no sight of poison in her body. So he got no idea of the suicide or the murder weapon . Sherlock couldn't make this out at all, so he waited a little bit more about this case.
Murder/Suicide 2 :- Their house had a ground outside . Another day turned out to be terrible for them. His brother Tarun was found dead this evening . His body was just lying on the ground . Sherlock Holmes was again called for this case .
Evidences :- To his surprise, he found a matchstick burnt out in his right-hand and a matchbox in his left-hand . The exactly same case for Rina but his hands are switched . His body was found lying on the ground . There was also a cigarette in his right-hand . The first to found his body was a neighbour of their family who came to the ground at first .
Sherlock found the matchbox to be the exact same matchbox which Rina had in her hand .
Interrogation :- Sherlock now asked all the neighbours of their house and found that everyday they and Tarun would meet in the ground and would do discussions , chats , etc . Most of them would smoke , and Tarun would also like to do smoking . However today Tarun was the $1$st to come in the ground , and on waiting for the other neighbours he probably suicided himself , or get murdered by someone .
On Interrogating with his family members , his mother, crying , said that she was only doing all the housework and is disheartened by seeing all this situations, his father was getting frustrated and furious and was only saying that he was sleeping, as he always liked to sleep. The maid was drying the clothes , the cook was cooking food for them, the milkman gave $3$ bottles of milk today again , and the watchman was guarding the frontgate (the frontgate did not face the ground , so the watchman did not face the ground.)
After hearing all this , Sherlock was totally confused , thinking deeply about the case in his home . Similarly, Sherlock didn't found out any bullet wounds , scratches , etc on his body too . Also there was no sight of poison in his body. So he again got no idea of the suicide or the murder weapon .
Murder/Suicide 3 :- Suddenly, the same night, the father was found lying dead in his bed. The mother found him dead , and Sherlock was called again. All thought someone murdered him while he was sleeping .
Evidence :- In this time , there was a matchstick burnt out on his right-hand and a lighter on his left hand . Besides him was a letter that read :-
"I always tried and tried, but I never succeeded in doing so. I don't want to live in this world. All my children died watching me. So I don't want to live here and I am committing suicide. "
After seeing this , Sherlock immediately understood the whole case, what happened and how it stood.
Can you find it? What exactly is this case and what happened then?
Giving you a hint to start with :-
Hint $1$ :- In every death the thing that was common is a matchstick . Perhaps it could be the murder/suicide weapon , but how can a matchstick kill someone?
Should I give a Hint $2$ ? That will reveal some more information :) . I will start a bounty if I get no answer for this . This is a mystery to think hard !
Here is a Hint $2$ then :-
Hint $2$ :- Are each of these deaths a suicide ? If it had been a murder , who do you think is the murderer then? Also what exactly do you think the father wanted to say in his letter? It's also possible that someone copied the letter himself and used a fake letter on his death , but it's upto you to think :) .