diff --git a/dockerfiles/Dockerfile.sandbox b/dockerfiles/Dockerfile.sandbox
index 516df05bd5..f097209335 100644
--- a/dockerfiles/Dockerfile.sandbox
+++ b/dockerfiles/Dockerfile.sandbox
@@ -67,3 +67,6 @@ ARG UWSGI_PROCESSES
 ENV UWSGI_PROCESSES=$UWSGI_PROCESSES
 
 ENV LISTEN_PORT=6000
+
+
+RUN echo "uwsgi_read_timeout 14400s;" > /etc/nginx/conf.d/custom_timeout.conf
\ No newline at end of file
diff --git a/nemo_skills/code_execution/local_sandbox/local_sandbox_server.py b/nemo_skills/code_execution/local_sandbox/local_sandbox_server.py
index 2d5938cd40..e0a4b311e5 100644
--- a/nemo_skills/code_execution/local_sandbox/local_sandbox_server.py
+++ b/nemo_skills/code_execution/local_sandbox/local_sandbox_server.py
@@ -22,6 +22,7 @@
 import tempfile
 import signal
 from io import StringIO
+import psutil
 
 from flask import Flask, request
 
@@ -29,6 +30,41 @@
 
 MEM_LIMIT_BYTES = int(os.environ.get('NEMO_SKILLS_SANDBOX_MEM_LIMIT', 10 * 1024 ** 3))  # 10 GiB default
 
+# Code to kill the process tree for lean4 code execution
+def kill_process_tree(proc):
+    """
+    Safely and aggressively kills a process and all its descendants.
+    This is the recommended approach for ensuring cleanup.
+    """
+    try:
+        parent = psutil.Process(proc.pid)
+        # Get all children of the process, recursively.
+        children = parent.children(recursive=True)
+        # Add the parent to the list of processes to be killed.
+        all_processes = children + [parent]
+        
+        # Kill all processes in the tree.
+        for p in all_processes:
+            try:
+                # SIGKILL is a forceful, non-ignorable kill signal.
+                p.kill()
+            except psutil.NoSuchProcess:
+                # The process might have already died, which is fine.
+                pass
+        
+        # Wait for all processes to be terminated.
+        gone, alive = psutil.wait_procs(all_processes, timeout=3)
+        if alive:
+            # If any processes are still alive, they are likely zombies
+            # or in an unkillable state. This is a last resort.
+            for p in alive:
+                print(f"Warning: Process {p.pid} could not be killed.")
+    except psutil.NoSuchProcess:
+        # The main process already died before we could kill it.
+        pass
+    except Exception as e:
+        print(f"Error in kill_process_tree: {e}")
+
 def set_limits(mem_bytes: int = MEM_LIMIT_BYTES) -> None:
     """
     Apply RLIMITs and start a new session for the child process.
@@ -79,33 +115,54 @@ def execute_python(generated_code, std_input, timeout, language):
 
 def execute_lean4(generated_code, timeout):
     temp_file_name = None
+    proc = None # <-- Keep track of the process object
     try:
         project_path = "/lean4/my_project"
+        # Use a with statement for the temp file to ensure it's closed
         with tempfile.NamedTemporaryFile(dir=project_path, delete=False, suffix=".lean") as temp_file:
             temp_file_name = temp_file.name
             temp_file.write(generated_code.encode('utf-8'))
+            temp_file.flush() # Ensure data is written to disk
 
-        result = subprocess.run(
+        # Use subprocess.Popen for more control
+        proc = subprocess.Popen(
             ['lake', 'env', '--dir', project_path, 'lean', temp_file_name],
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
-            timeout=timeout,
-            cwd=project_path,  # Ensure we are in the correct working directory
+            cwd=project_path,
+            preexec_fn=os.setsid
         )
 
-        if result.returncode == 0:
+        # Communicate with the process, which waits for it to finish
+        # This will raise TimeoutExpired if the timeout is reached
+        stdout, stderr = proc.communicate(timeout=timeout)
+
+        if proc.returncode == 0:
             process_status = "completed"
         else:
             process_status = "failed"
 
         return {
             "process_status": process_status,
-            "stdout": result.stdout.decode('utf-8'),
-            "stderr": result.stderr.decode('utf-8'),
+            "stdout": stdout.decode('utf-8'),
+            "stderr": stderr.decode('utf-8'),
         }
 
     except subprocess.TimeoutExpired:
-        return {"process_status": "timeout", "stdout": "", "stderr": "Timed out\n"}
+
+        # kill the process tree
+        kill_process_tree(proc)
+        
+        # Now we can safely get any output that was generated before the kill.
+        stdout, stderr = proc.communicate()
+
+        final_stderr = stderr.decode('utf-8') + "Timed out\n"
+        return {
+            "process_status": "timeout",
+            "stdout": stdout.decode('utf-8'),
+            "stderr": final_stderr,
+        }
+
     except Exception as e:
         print(f"Error: {str(e)}")
         return {"process_status": "error", "stdout": "", "stderr": str(e) + "\n"}
@@ -149,4 +206,4 @@ def execute():
 if __name__ == '__main__':
     log = logging.getLogger('werkzeug')
     log.setLevel(logging.WARNING)
-    app.run(port=6000)
+    app.run(port=6000)
\ No newline at end of file
diff --git a/requirements/code_execution.txt b/requirements/code_execution.txt
index 546492f7fe..4095a94b07 100644
--- a/requirements/code_execution.txt
+++ b/requirements/code_execution.txt
@@ -23,3 +23,4 @@ pandas
 scipy
 sympy
 tqdm
+psutil
\ No newline at end of file